Fuel composition

ABSTRACT

There is described a fuel composition incorporating levulinic acid or a functional derivative thereof.

[0001] The use of surfactants as additives for fuels has long beenknown. Thus, for example, British Patent GB 2 21 72 29 describes anadditive which contains 48 parts by volume of an ethoxylated alcohol, 3to 8 parts of lauric acid diethanolamide, 3 to 8 parts of oleic aciddiethanolamide and 1.5 to 4 parts of an ethoxylated oleic acid. Suchcompositions are suitable as additives which permit the dissolution ofwater in fuel and thus reduce the corrosion. However, problems arisewhen, instead of the water, for example short-chain alcohols are to beused as the mixed phase with the fuels. For this purpose, WO 98/17745describes an alternative composition which contains 25% by volume ofdiethanolamide, 50% by volume of an ethoxylated alcohol and 25% byvolume of a C₁₄ fatty acid ethoxylated with 7 mol ethylene oxide permole of fatty acid. The additive is used for improving the solubility ofethanol in diesel, which in the end results in the reduction in theemissions of CO₂ and CO and NO_(x) and particulate matter (PM) when thefuel is burned in a compression-ignition engine.

[0002] As in the past, the disadvantage is that a large number ofindividual substances have to be used to achieve the desired effect.There has long been a need for achieving dissolution of alcohol in fuel,preferably in diesel, by using economical additives which are as simpleas possible, in order to achieve in this way a noticeable reduction ingaseous reaction products of combustion, in particular NO. and CO or CO₂and PM.

[0003] It is an object of the invention to provide a fuel compositionwhich incorporates an additive which (a) provides more oxygen by volumethan ethanol or traditional oxygenates such as MTBE or ETBE and (b)gives little or no increase in fuel Reid vapour pressure (RVP) and (c)has little or no effect on the flash point of the base fuel. As a resulta fuel composition of this invention will provide significant calorificpower with few emissions on combustion in automotive engines, whilstexhibiting low Reid vapour pressure and maintaining the flash point ofthe base fuel.

[0004] According to the invention in one aspect there is provided a fuelcomposition incorporating levulinic acid, or a functional derivativethereof.

[0005] The functional derivative will be one which has no side effectsin the context of a fuel composition. Preferably the derivative is analkyl derivative; preferably one having from 1 to 10 carbon atoms.Preferred is ethyl levulinate. Alternatively, methyl levulinate may beused.

[0006] Thus according to one aspect of the invention we provide a fuelcomposition which is substantially free of alkanolamides, containing atleast 95% by volume of a hydrocarbon-based fuel and from 0.1 to 5% byvolume of levulinic acid, or a functional derivative thereof

[0007] A composition of the invention can incorporate hydrocarbon fuelssuch as gasolines and diesels together with other additives one of whichis preferably a blend of non-ionic surfactants including the additivedescribed and claimed in International patent application PCT/GB97/02763which is incorporated herein by reference.

[0008] Furthermore, specific fuel compositions which may be preferredare those disclosed in co-pending International Patent applications Nos.PCT/GB01/04947 and PCT/GB01/04934 which are incorporated herein byreference.

[0009] Thus according to one aspect of the invention we provide a fuelcomposition which is substantially free of alkanolamides, containing atleast 95% by volume of a hydrocarbon-based fuel and from 0.1 to 5%. byvolume of levulinic acid, or a functional derivative thereof and from0.1 to 5% by volume of an additive selected from the groups consistingof:

[0010] a) the optionally alkoxylated linear or branched saturated orunsaturated monoalcohols having 8 to 24 C atoms, containing zero or 1 to20 mol of ethylene oxide and/or 1 to 5 mol of propylene oxide per mol ofalcohol, or

[0011] b) the polyols having 2 to 6 carbon atoms, optionally partiallyesterified with fatty acids having 12 to 24 carbon atoms, or

[0012] c) the alkoxylated fatty acids having 12 to 24 carbon atoms and 4to 20 mol of ethylene oxide per mol of fatty acid, or

[0013] d) the ethoxylated dimeric fatty acids.

[0014] In this aspect of the invention, the fuel composition comprisescomponent a).

[0015] Component a)

[0016] Fatty alcohols are to be understood as a meaning primaryaliphatic alcohols of the formula (I)

R¹OH   (I)

[0017] in which R¹ represents an aliphatic, linear or branchedhydrocarbon radical having 8 to 24 carbon atoms and 0 and/or 1, 2 or 3double bonds. Typical examples are caproic alcohol, caprylic alcohol,2-exthylhexyl alcohol, capric alcohol, lauryl alcohol, isotridecylalcohol, myristyl alcohol, cetyl alcohol, palmoleyl alcohol, stearylalcohol, isostearyl alcohol, oleyl alcohol, elaidyl alcohol,petroselinly alcohol, linolyl alcohol, linolenyl alcohol elaeostearylalcohol, arachyl alcohol, gadoleyl alcohol, behenyl alcohol, erucylalcohol and brassidyl alcohol and their industrial mixtures which areobtained, for example, in the high-pressure hydrogenation of industrialmethyl esters based on fats and oils or aldehydes from Roelen's oxosynthesis and as a monomer fraction in the dimerisation of unsaturatedfatty alcohols. Industrial fatty alcohols having 12 to 18 carbon atoms,such as, for example, coconut fatty alcohol, paln fatty alcohol, palmkernel fatty alcohol or allow fatty alcohol, are preferred. Oleylalcohol is particularly preferred. Guerbet alcohols having 12 to 16carbon atoms are furthermore preferred.

[0018] The use of the alkoxylated, preferably ethoxylated and/orpropoxylated derivatives of the fatty alcohols of the formula (I) isalso particularly preferred. The preparation of these compounds is knownand is carried out, for example, by reacting the fatty alcohols in thepresence of acidic or basic catalysts with ethylene oxide and/orpropylene oxide. Preferred adducts contain 1 to 20 mol of ethyleneand/or 1 to 5 mol of propylene oxide per mol of fatty acid. Alkoxylatedalcohols which contain 1 to 20 mol of ethylene oxide per mol of fattyalcohol and are free of propylene oxide are particularly preferred. Itis furthermore preferable if the radical R represents unsaturated C₁₂₋₁₈radical. A fatty alcohol ethoxylated with 8 mol of ethylene oxide is tobe regarded as a further particularly preferred compound a).

[0019] According to a second aspect of the invention the fuel additivecomprises component b).

[0020] Component b)

[0021] In addition to the mono alcohols, polyols and their esterifiedderivatives are also suitable additives for the fuel according to theinvention. Polyols are organic compounds having 2 to 8 carbon atoms and2 to 4 hydroxyl functions per molecule. These include, for example,ethylene glycol, propylene glycol, butylene glycol and their oligomers,for example butylene diglycol. Another preferably used polyol isglycerol Furthermore, neopentyl compounds, such as pentaeryt ritol ortrimethylolpropane, are suitable components for group b). The partiallyesterified derivatives of the polyols, for example glycerol mono-and/ordiesters with fatty acids having 8 to 22 carbon atoms, are furthermorepreferred. Particularly preferred esters are pentaerytlbrityl esterspartially esterified with the fatty acids. Other derivatives, such asethers, for example diethylene glycol monobutyl ether, are alsosuitable.

[0022] According to a furter aspect of the invention the fuel additivecomprises component c).

[0023] Component c)

[0024] The compositions according to the invention contain alkoxylatedfatty acids as component c). These fatty acid alkoxylates are knowncompounds and can be prepared by all methods known to a person skilledin the art. The fatty acid alkoxylates contained in the compositionsaccording to the invention contain exclusively ethylene oxide groups asalkoxides. They preferably contain between 4 and 20 mol of ethyleneoxide and in particular 2 to 10 mol of ethylene oxide per mol of ester.

[0025] The fatty acid components used are fatty acids have 5 to 30 Catoms and of natural or synthetic origin, in particular straight-chain,saturated or unsaturated fatty acids, including industrial mixturesthereof, as obtainable by lipolysis from animal and vegetable fats andoils, for example from coconut oil, palm kernel oil, soya oil, sunfloweroil, colza oil, cottonseed oil, fish oil, beef tallow, and lard;specific examples are caprylic, capric, lauric, lauroleic, myristic,myristoleic, palmitic, palmitoleic, oleic, elaidic, arachic, gadoleic,behenic, and erucic acid.

[0026] According to a further aspect of the invention the fuel additivecomprises component d).

[0027] Component d)

[0028] The oligomerisation of unsaturated fatty acids is a knownelectrocyclic reaction reported in review articles, for example by A.Behr in Fat Sci, Techno. 93, 340 (1991), G. Spiteller in Fac Sci,Technol 94, 41 (1992) or P. Daute et al, in Fat Sci, Technol, 95, 91(1993). In the oligomerisation, on average two or three fatty acidscombine and form dimers or trimers, which have predominantlycycloaliphatic structures. In addition to the fraction comprising thedimers and trimers, a so-called monomer fraction is obtained, whichcontains unconverted starting materials and branched monomers which havebeen formed by isomerisation in the course of the reaction. In addition,there is of course also a fraction of higher oligomers which, however,is generally not very important The oligomerisation can be carried outthermally or in the presence of noble metal catalysts. Preferably, thereaction is carried out in the presence of clays, such as, for example,montmorillonite. The content of dirners and trimers or the amount ofmonomer fraction can be regulated by the reaction conditions. Industrialmixtures can finally also be purified by distillation. Suitable startingmaterials for the oligomerisation are industrial unsaturated fatty acidshaving 12 to 22, preferably 16 to 18, carbon atoms. Typical examples arepalmitoleic acid, oleic acid, elaidic acid, petroselinic acid, linoleicacid, linolenic acid, conjuenic fatty acid, elaeostearic acid,ricinoleic acid, gadoleic acid, erucic acid, and their industrialmixtures with saturated fatty acids. Typical examples of suitableindustrial mixtures are unhydrogenated cleavage fatty acids or naturaltriglycerides having iodine numbers in the range from 40 to 140, suchas, for example, palm oil acid, tallow fatty acid, colza fatty acid,sunflower fatty acid and the like. Cleavage fatty acids having a highercontent of oleic acid are preferred.

[0029] In addition to the fatty acids , it is possible to dimerise theiresters, preferably methyl esters. It is also possible to oligomerise theacid and to convert it into the methyl esters prior to hydrogenation.The conversion of the ester group into the acid group takes place in amanner knownper se.

[0030] Dimeric fatty acids, which are particularly preferred in thecontext of the present invention, are obtained by oligomerisation ofindustrial oleic acid and preferably have a dimer content of 50 to 99%by weight and a polymer content (including trimer content) of 1 to 50%by weight. The content of monomers may be 1 to 15% by weight and, ifrequired, may be reduced by distillation. Dimeric fatty acids which areobtained by oligomerisation are industrial oleic acid and have a dimercontent of 70 to 85% by weight, a polymer content of 10 to 20% by weightand a monomer content of 5 to 15% by weight are particularly preferred.The percentages by weight are based on the total amounts of dimericfatty acid.

[0031] The content of the levulinic acid, or a functional derivativethereof, may vary, but may be low, such as from 2 to 5% by volume, anexample being about 4% by volume. This is significantly lower than otheradditives which contain oxygen. Such additives may, however, also bepresent and examples include water.

[0032] According to a further aspect of the invention, thehydrocarbon-based fuel may be substantially alcohol free. Such alcoholsare preferentially C1 to C6 alkanols, such as propanol, butanol orethanol, and isomers thereof. By the term alcohol free we mean, forexample, less than 0.01% by volume alcohol.

[0033] The fuel compositions according to the invention are prepared bymixing levulinic acid, or a functional derivative thereof and thecomponents a), b), c) or d) individually with a fuel. Preferred fuelcompositions are those in which the volume ratio (v/v) of fuel, e.g.petroleum diesel to additive is in the range of 1000:0.5 to 1000:50, andpreferably of 1000:1 to 1000:50.

[0034] In a preferred embodiment of the invention we provide a fuelcomposition consisting of 93 to 99.4% by volume of diesel oil from 0.1to 5% by volume of levulinic acid, or a functional derivative thereofand 0.5 to 2% by volume of an additive a), b), c) or d) according to theabove description.

[0035] The use of the additives according to the invention makes itpossible to prepare mixtures of fuels with levulinic acid ashereinbefore described, preferably petroleum diesel, in an economicalmanner. Preferably, a maximum of 0.5 to 2.0% by volume of additive areadded to the diesel oil/levulinic acid mixture. Water may also bepresent. water content may be less than 0.2% volume, preferably lessthan 0.11% by volume.

[0036] According to a second aspect of the invention we provide a fuelcomposition which is substantially free of alkoxylated compounds and issubstantially free of long-chain alkyl alcohols having at least 6 Catoms, and contains at least 95% by volume of a hydrocarbon-based fuel,from 0.1 to 5% levulinic acid, or a functional derivative thereof, and0.1 to 5% by volume of an additive of the formula (I);

R—CO—NR¹R²   (I)

[0037] in which R is a saturated or unsaturated, linear or branchedalkyl radical having 6 to 21 C atoms; and

[0038] R¹ and R², which may be the same or different, each represent ahydroxyalkyl radical having 1 to 4 C atoms.

[0039] In a yet further aspect of the invention the fuel additive maycomprise an oleic alkanolamide and an alkoxylated oleic acid.

[0040] One advantage of the composition of the invention is that, interalia, all of the ingredients are substantially or totally miscible, as aresult of which, the composition has clarity and long term stability.The use of levilinic acid, or a derivative thereof avoids the necessityto use ethanol as an oxygenator.

[0041] In another aspect the fuel is diesel or gasoline. When diesel ispresent the composition becomes one which is of the type which may alsoinclude biodiesel, made from renewable feedstock sources. A suitablecomposition may contain for example materials such as rape-seed fattyacid methyl esters, soya fatty acid methyl esters, recyclable cookingoils and fats.

[0042] International Patent Application No. WO99/35215, Wenzel,describes an additive for combustible fuels which includes a nitrogensource, such as urea. Whilst the additive is said to reduce NOx, thecompositions are very complex and include numerous ingredients,including:

[0043] a water soluble alcohol,

[0044] a C6 to C12 alcohol

[0045] a C6 to C18 ethoxylated alcohol

[0046] a C10 to C24 fatty acid, and

[0047] a nitrogen source.

[0048] We have now surprisingly found that.the fuel composition of theinvention can comprise very low fuel: additive ratios in combinationwith nitrogenous compounds, such as urea.

[0049] Thus according to the invention we provide a fuel composition ashereinbefore described and a nitrogen source.

[0050] The nitrogen compound may be selected from the group consistingof ammonia, hydrazine, alkyl hydrazine, dialkyl hydrazine, urea,ethanolamine, monoalkyl ethanolamine, and dialkyl ethanolamine whereinalkyl is independently selected from methyl, ethyl, n-propyl orisopropyl. Urea is preferred. The nitrogen compound may be an anhydrouscompound or a hydrous compound, e.g. an aqueous solution, and may be upto a 5% w/w aqueous solution.

[0051] According to a yet further feature of the invention we provide amethod of solubilising a nitrogen compound in a fuel composition whichcomprises mixing a hydrocarbon fuel, a nitrogen compound and a fueladditive as hereinbefore described. The method of the invention mayoptionally include the addition of an alcohol, such as ethanol or water,as hereinbefore described.

[0052] We also provide the use of a nitrogen compound in the manufactureof a fuel additive of this aspect of the invention. We especiallyprovide the use of urea in the manufacture of fuel additive of theinvention.

[0053] In the fuel composition in this aspect of the invention thenitrogen compound may be added by being incorporated into the fueladditive or may be added separately. Furthermore, the nitrogen compoundmay be added as an aqueous solution.

[0054] The fuel composition of the invention may also optionallycomprise a cetane booster in amount of from 0.1% v/v to 1.0% v/v, basedon the volume of the mixture. When a cetane booster is included in thefuel composition of the invention it may be added as part of the fueladditive of the invention or it may be added separately.

[0055] A suitable cetane booster for use in the mixture is selected fromthe group comprising, 2-ethylhexyl nitrate, tertiary butyl peroxide,diethylene glycol methyl ether, cyclohexanol, and mixtures thereof Theamount of cetane booster present in the mixture is a function of thecetane value of the particular diesel fuel and the amount of ethanolpresent in the particular fuel composition. Generally, the lower thediesel fuel cetane value, the higher the amount of the cetane booster,similarly, because ethanol typically acts as a cetane depressant, thehigher the concentration of ethanol in the solution, the more cetanebooster may be necessary in the mixture.

[0056] The fuel additives of the invention are advantageous in that,inter alia, they are more efficient at producing micro emulsions thanprior art additives. Therefore, they are capable of more efficientlyproducing a stable, clear and homogenous solution with a hydrocarbonfuel, e.g. diesel/ethanol, even in the presence of water. Therefore,according to a further feature of the invention we provide a fuelcomposition as hereinbefore described, which optionally includes anamount of water, and wherein the fuel consists of a substantiallystable, clear and substantially homogeneous solution.

[0057] Furthermore, the fuel additive or the fuel composition of theinvention may also optionally include a demulsifier in an amount of lessthan 5% v/v and preferably less than 1% v/v based on the volume of themixture.

[0058] When bio-diesel type fuel is used the properties offossil-derived diesel fuel are obtained, but there is less pollution.Oxygenated diesels combust in automotive engines to generate less toxicexhaust gases than non-oxygenated diesels such as the oxides ofnitrogen, carbon monoxide and particulate matter.

[0059] According to a further aspect of the invention we provide amethod of running an internal combustion engine comprising the use of afuel composition as hereinbefore described.

[0060] We also provide the use of levulinic acid, or a functionalderivative thereof, in the manufacture of a fuel composition ashereinbefore described.

[0061] Blends of ethanol as oxygenate with gasoline, whilst improvingcombustion of the hydrocarbons and reducing toxic gas emissions, exhibitincreased Reid vapour pressure. Such increases are undesirable in thatthe RVP of the blend may exceed the limits specified for commercialautomotive fuels for example 7.0 psi in the USA Envirornental ProtectionAgency specification when tested according to ASTM D 5191-99.

[0062] Blending of gasoline with levulinic acid or derivatives such asesters produces oxygenated fuels with RVP similar to that of the basegasoline. Low RVP blends are specified during the warmer seasons and theability to produce oxygenated gasoline without increasing RVP opens upfurther blending options for the refinery.

[0063] Diesels can be blended with ethanol as oxygenate to produceoxygenated diesels which combust more effectively than the base dieselsin compression ignition engines and give lower yields of toxic emissionson combustion. However, such blends exhibit flash points similar to thatof ethanol i.e. typically 15° C., and consequently they require handlingand storage in a similar way to gasoline fuels.

[0064] When levulinic acid or derivatives are blended in as oxygenatewith diesels, the flash point of the blends remains un-affected and suchoxygenated diesels can be handled and stored in the same way as diesels.

[0065] The foregoing is illustrated by the following examples.

[0066] Testing Protocols

[0067] Gasolines

[0068] ASTM Standard D 5191-99 describes the standard test fordetermining the vapour pressure of petroleum products by the Reidmethod. In the USA, the Environment Protection Agency specifies 7 psi asthe maximum allowable RVP in gasoline fuels. In Europe, EN228:2000specifies a maximum RVP of 60-70 kPa in summer.

[0069] Specification gasoline blends containing up to 5.0% ethyllevulinate, 1.0% water and 2.0% non-ionic surfactant were found to havesimilar RVPs to the base gasoline.

[0070] Diesels

[0071] ASTM D93 describes the standard test method for determining theFlash Point of fuels. The minimum flash point required to comply withthe US Specification ASTM D975 for diesel fuels is 52° C. for No.2diesel and 38° C. for No.1 diesel. In Europe, EN590 specifies a minimumof 55° C.

[0072] Specification diesel blends containing up to 5.0% ethyllevulinate, 1.0% water and 2.0% non-ionic surfactant were found to havesimilar flash points to the base diesel.

1. A fuel composition incorporating levulinic acid, or a functionalderivative thereof.
 2. A fuel composition according to claim 1characterised in that the levulinic acid, or a functional derivativethereof is an alkyl levulinate.
 3. A fuel composition according to claim2 characterised in that the alkyl group has from 1 to 10 carbon atoms.4. A fuel composition according to claim 3 characterised in that thealkyl levulinate is ethyl levulinate.
 5. A fuel composition according toclaim 3 characterised in that the alkyl levuliiate is methyl levulinate.6. A fuel composition according to claim 1 characterised in that thecomposition includes one or more additional fuel additives.
 7. Acomposition according to claim 6 characterised in that the compositionis substantially free of alkanolamides.
 8. A fuel composition accordingto claim 7 characterised in that the composition contains at least 95%by volume of a hydrocarbon-based fliel and from 0.1 to 5% by volume oflevulinic acid, or a functional derivative thereof and from 0.1 to 5% byvolume of an additive selected from the groups consisting of: a) thealkoxylated linear or branched saturated or unsaturated monoalcoholshaving 8 to 24 C atoms, containing zero or 1 to 20 mol of ethylene oxideand/or 1 to 5 mol of propylene oxide per mol of alcohol or b) thepolyols having 2 to 6 carbon atoms, optionally partially esterified withfatty acids having 12 to 24 carbon atoms, or c) the alkoxylated fattyacids having 12 to 24 carbon atoms and 4 to 20 mol of ethylene oxide permol of fatty acid, or d) the ethoxylated dimeric fatty acids.
 9. Acomposition according to claim 8 characterised in that component a) isselected from the group of primary aliphatic alcohols of the formula (I)R¹OH   (I) in which R¹ represents an aliphatic, linear or branchedhydrocarbon radical having 8 to 24 carbon atoms and 0 and/or 1, 2 or 3double bonds.
 10. A fuel composition according to claim 9 characterisedin that the primary aliphatic alcohol is selected from the group caproicalcohol, caprylic alcohol, 2-exthylhexyl alcohol, capric alcohol, laurylalcohol, isotridecyl alcohol, myristyl alcohol, cetyl alcohol, paimoleylalcohol, stearyl alcohol, isostearyl alcohol, oleyl alcohol, elaidylalcohol, petroselinly alcohol, linolyl alcohol, linolenyl alcohol,elaeostearyl alcohol, arachyl alcohol, gadoleyl alcohol, behenylalcohol, crucyl alcohol and brassidyl alcohol.
 11. A fuel compositionaccording to claim 9 characterised in that the alcohol is selected fromthe group coconut fatty alcohol, palm fatty alcohol, palm kernel fattyalcohol or to allow fatty alcohol.
 12. A fuiel composition according toclaim 9 characterised in that the alcohol is oleyl alcohol.
 13. A fuelcomposition according to claim 9 characterised in that alcohol is one ormore of the Guerbet alcohols having 12 to 16 carbon atoms.
 14. Acomposition according to claim 8 characterised in that component b) isselected from the group including ethylene glycol, propylene glycol,butylene glycol and their oligomers, for example butylene diglycol. 15.A composition according to claim 8 characterised in that component b) isglycerol.
 16. A composition according to claim 8 characterised in thatcomponent b) is selected from the group including neopentyl compounds,such as pentaerythritol or trimethylolpropane.
 17. A compositionaccording to claim 8 characterised in that component b) is selected fromthe group including the glycerol mono-and/or diesters with fatty acidshaving 8 to 22 carbon atoms.
 18. A composition according to claim 8characterised in that component b) is selected from the group includingpentaerytlrityl esters partially esterified with the fatty acids.
 19. Acomposition according to claim 8 characterised in that component b) is adiethylene glycol monobutyl ether.
 20. A fuel composition according toclaim 1 characterised in that component c) is selected from the groupincluding ethylene oxide groups as alkoxides.
 21. A fuiel compositionaccording to claim 20 characterised in that component c) containsbetween 4 and 20 mol of ethylene oxide.
 22. A fluel compositionaccording to claim 21 characterised in that component c) contains 2 to10 mol of ethylene oxide per mol of ester.
 23. A fuel compositionaccording to claim 8 characterised in that the fatty acid components ofcomponent c) are fatty acids having 5 to 30 C atoms and of natural orsynthetic origin, in particular straight-chain, saturated or unsaturatedfatty acids, including industrial mixtures thereof, as obtainable bylipolysis from animal and vegetable fats and oils, for example fromcoconut oil, palm kernel oil, soya oil, sunflower oil, colza oil,cottonseed oil, fish oil, beef tallow, and lard; specific examples arecaprylic, capric, lauric, lauroleic, myristic, myristoleic, palmitic,palmitoleic, oleic, elaidic, arachic, gadoleic, behenic, and erucicacid.
 24. A fuel composition according to claim 8 characterised in thatcomponent d) is selected from dimers of the group palmitoleic acid,oleic acid, elaidic acid, petroselmic acid, linoleic acid, linolenicacid, conjuenic fatty acid, elaeostearic acid, ricinoleic acid, gadoleicacid, erucic acid, and their industrial mixtures with saturated fattyacids.
 25. A fuel composition according to claim 8 characterised in thatcomponent d) is selected from dimers of the group, palm oil acid, tallowfatty acid, colza fatty acid and sunflower fatty acid.
 26. A fuelcomposition according to claim 8 characterised in that component d) is adimer of oleic acid.
 27. A fuel composition according to claim 1characterised in that the composition is substantially free ofalkoxylated compounds and is substantially free of long-chain alkylalcohols having at least 6 C atoms, and contains at least 93% by volumeof a hydrocarbon-based fuel, from 0.1 to 5% levulinic acid, or afunctional derivative thereof, and 0.1 to 2% by volume of an additive ofthe formula (I); R—CO—NR¹R²   (I) in which R is a saturated orunsaturated, linear or branched alkyl radical having 6 to 21 C atoms;and R¹ and R², which may be the same or different, each represent ahydroxyalkyl radical having 1 to 4 C atoms.
 28. A fuel compositionaccording to claim 1, characterised in that the composition includes anester of rape-seed or soya fatty acid.
 29. A fuel composition accordingto claim 1 characterised in that the fuel is gasoline.
 30. A compositionaccording to claim 1 characterised in that the fuel is Diesel.
 31. Afuel composition according to claim 29 characterised in that the ReidVapour Pressure is similar to that of the base gasoline.
 32. A fuelcomposition according to claim 30 characterised in that the flash pointis similar to that of the base diesel.
 33. A method of running aninternal combustion engine comprising the use of a fuel compositionaccording to claim
 1. 34. A fuel composition according to claim 1characterised in that it includes a nitrogen compound selected from thegroup consisting of ammonia, hydrazine, alkyl hydrazine, dialkylhydrazine, urea, ethanolamine, monoalkyl ethanolamine, and dialkylethanolamine wherein alkyl is independently selected from methyl, ethyl,n-propyl or isopropyl.
 35. A fuel composition according to claim 1characterised in that the composition includes a cetane booster inamount of from 0.1% v/v to 1.0% v/v, based on the volume of the mixture.36. A fuel composition according to claim 35 characterised in that thecetane booster is selected from the group comprising, 2-ethylhexylnitrate, tertiary butyl peroxide, diethylene glycol methyl ether,cyclohexanol, and mixtures thereof.
 37. A fuel composition according toclaim 1 characterised in that the optionally composition includes ademulsifier in an amount of less than 5% v/v and preferably less than 1%v/v based on the volume of the mixture.
 38. A fuel composition accordingto claim 1 characterised in that the composition includes water.
 39. Acomposition according to claim 6 characterised in that the additivecomprises a fatty acid diethanolamide, an ethoxylate of a long chainfatty acid and optionally an alcohol ethoxylate, the degrees ofethoxylation being selected so that a long term stable fuel compositionis formed.
 40. A fuel composition according to claim 29 characterised inthat the composition comprises 92-97.5% gasoline, 2-5% ethyl levulinate,0-1% water and 0.5-2% of a fuel additive.
 41. The use of levulinic acid,or a functional derivative thereof, in the manufacture of a fuelcomposition according to claim
 1. 42. A fuel composition substantiallyas described with reference to the accompanying examples.